This invention relates generally to the manufacture of thin film and, more particularly, to the winding of such film into rolls of high quality.
Equipment for winding rolls from a continuous length of film is available and in use. It is known that bowed rolls and/or spreader bars can be used in advance of the windup to flatten the film. Although such devices spread the film in transport, additional defects are introduced in the actual winding process. For example, as film is advanced to a roll, boundary air is entrapped and compressed slightly between the outside film layers and moves to regions between high spots or gage bands. This compressed air increases the diameter of the roll slightly where the film layers are thinnest. Resulting bubble-like areas reduce the laydown width. When the air bleeds to atmosphere, the affected film layers fold into wrinkles in the machine direction (MD). It is difficult, if not impossible, to avoid prominent, unacceptable wrinkles when winding ultra-thin film according to standard methods. Such wrinkles have an adverse effect on yield insofar as they present difficulties in achieving uniformity in subsequent coating, metallizing and laminating steps.